This invention relates to needleless injector cartridges.
Needleless injectors are used as an alternative to conventional hypodermic syringes for injecting liquid medicaments into the tissues of a patient. The usual principle of operation is a high pressure piston pump which propels a jet of liquid with sufficient force to penetrate the epidermis and deposit in the underlying tissues. Such devices have been available for over fifty years and most examples are multi-dose devicesxe2x80x94that is, a succession of doses may be drawn from a reservoir, each dose being dispensed from an integral pressure chamber. The motive force may be derived from stored electrical, manual, pyrotechnic or pressurised gas energy.
In the 1980""s, there were some reports of cross contamination through using multi-dose injectors, which promoted a search for safer ways, and a variety of injectors were invented comprising a multi-dose power unit or actuator, to which a disposable injection cartridge could be fixed. These cartridges were usually intended to be filled by the user with the aid of a transfer device, by which means a medicament could be drawn from a vial and transferred to a cartridge. There are a number of problems arising from this approach: it is practically impossible to achieve aseptic transfer of the medicament; there is likelihood of significant amounts of trapped air bubbles in the cartridge which reduce injection performance; and there is a chance of preparing an incorrect amount to be injected. A few attempts were made to supply prefilled cartridges, but most materials proposed for the cartridges were unsuitable for long-term contact with the medicament, or at least would require extensive and costly validation for each application.
The ideal material for most applications is borosilicate glass, because it has the required inertness, transparency, and barrier properties. However, the pressures reached in needleless injectors can be very highxe2x80x94in the order of 600 barsxe2x80x94and a cartridge to be made from glass requires very careful design and processing in order to avoid breakage. Our co-pending application published under No. WO 98/13086 describes a method of manufacturing glass needleless injector cartridges, but the process requires a large investment in specialised plant in order to achieve the low component cost necessary for many applications.
Some drugs cannot be stored for long periods in glass however, and therefore have to be stored in some other material. In such cases, that other material will still be unlikely to withstand the high injection pressures.
The present invention seeks to overcome the drawbacks of prior art devices by providing a needleless injector cartridge which includes a liquid medicament reservoir as an attached part thereof, with means to transfer the liquid from the reservoir into the part of the cartridge from which injection takes place.
In accordance with the invention there is provided a needleless injector cartridge, comprising:
an injection component defining a void therein for receiving medicament, and having an injection discharge orifice communicating with the void; and
a transfer device comprising a liquid-containing reservoir, and transfer means for causing the liquid to flow from the reservoir, through a reservoir outlet, into said void.
Preferably the reservoir is made of glass, but other materials may be used if glass is unsuitable for long term storage contact with the medicament. The injection component may be of a material suitable for short term contact with the medicament, and suitable for the extremely high injection pressures. Stainless steel or liquid crystal polymer are two diverse materials which would be suitable, or a combination of materials may be used to optimise the requirements of cost, performance and sizexe2x80x94for example an inexpensive polypropylene cartridge may be housed in a steel casing, the latter providing support for the plastic during the injection.
In a first preferred embodiment there is provided plastic injection component which is preferably a cylinder containing a piston, and which has a small discharge orifice at one end. Attached, preferably coaxially, to the injection component at the discharge end is an open cylinder into which is placed a reservoir made from a material compatible with the medicament contained therein. The reservoir has a sharp discharge tube at one end, and the other contains a plunger, with the medicament contained between the plunger and discharge tube. An elastomeric seal surrounds and seals on the outside of the discharge tube and also seals against the discharge orifice of the injection component. The seal provides a conduit between the reservoir and injection component, but is temporarily blocked by a septum. The piston in the injection component is located so as to permit the latter to receive the required volume of liquid, and the void between the piston and septum is evacuated. A screw cap on the reservoir holder acts on the plunger in the reservoir, so that when the cap is rotated the plunger drives the reservoir forward until the reservoir discharge tube perforates the septum. Continued movement of the cap dispenses the required volume of medicament from the reservoir into the injection component. The reservoir holder, reservoir, plunger and cap are then detached together and the filled injection component is ready for use. The use of the screw cap enables the user to move the plunger steadily, in a manner which avoids any sudden jerks, thus reducing the possibility of the liquid undergoing undesirable foaming. It also means that a greater force be exerted on the plunger, so enabling a larger diameter plunger to be used than would otherwise be the case. That in turn means that the reservoir can be shorter, so helping to keep the overall length of the transfer device short. The cartridge may be attached to a multi-use actuator or a single use device, or have been pre-assembled to such before filling.
A second preferred embodiment provides a device for transferring a liquid as described in the first preferred embodiment, wherein a lyophilised (freeze dried) drug or other dry material is held within the evacuated injection component, and the transfer of liquid in the described manner dissolves the material so that it may be injected.
A third preferred embodiment is similar to the first, except that the reservoir is fitted with two plungers, spaced apart, and containing the liquid within the space. Forward movement of the plungers brings the liquid up to one or more bypass grooves in the wall of the reservoir, so that the liquid passes through the grooves and into the injection component.
In all of the embodiments described above there is a vacuum within the cartridge, so that the chance of a large gas bubble being trapped is reduced when the liquid is transferred. The piston within the injection component is held in position with sufficient friction to prevent its movement due to the pressure differential. If the existence of bubbles is not particularly important, then a fourth embodiment has the piston placed initially near to the injection discharge orifice of the injection component and when the content of the reservoir is transferred, the piston moves in response to the hydraulic pressure created by the transfer mechanism. This embodiment does not require evacuation of the drug chamber before filling, but if it is necessary to reduce trapped air to a very small volume, evacuating the void within the capsule before filling will achieve this objective.